The revelation was as shocking as it was incomprehensible: Someone in Bel-Air used 11.8 million gallons of water in a single year.

Appalled officials had no choice but to react when they found out last fall. Councilman Paul Koretz called the consumption “a slap in the face to neighbors” who had conserved during four years of drought and demanded that the Department of Water and Power explain how it planned to deal with such “irresponsible” users.

Now, more than five months later, the city’s water utility has unveiled its plan to punish its most wasteful residents with hefty fines.

“We have to come to you, determine what you’re doing wrong, and then you have to continue to violate to be exposed to these fines,” said Marty Adams, DWP’s senior assistant general manager in charge of the water system. “But if we have these mega-users who are like that — and money is no object — this provides us a tool to fine them.”

DWP’s board of commissioners will consider the plan Wednesday, one day after the City Council approved a rate increase that is expected to provide more than $1 billion over five years, largely for water and electricity system upgrades. Water rates will increase 4.7% and power rates will go up 3.86% each year, starting as early as mid-April.

Currently, the department can fine only customers who violate a specific provision of the city’s water ordinance, such as watering at the wrong time of day or using a hose to wash down a driveway. The fines are relatively small, ranging from $100 to $300 while the city is in any phase of its water conservation plan.

Under the new proposal, fines would increase with each phase of the plan to as much as $1,200 in Phase 5. And the amendments to the ordinance would establish a new system to address what the department calls “unreasonable use” during serious phases of drought. The fines for that behavior would start at $1,000 a month and go as high as $40,000 a month.

“The idea is to be fair. We could have had a straight cutoff [for water use], but there are very different living situations in the city,” Adams said. “Ultimately, the goal is still not to penalize people. The goal is to get people to comply and save water.”

The customers who find themselves chronically in the highest water-use tier will be subject to a water-use analysis by DWP, Adams said.

Customers under audit will have to provide staff members with access to their property and “fully cooperate,” according to a letter prepared for the DWP board. After the analysis is complete, staff members will prepare a conservation plan that spells out ways to reduce water waste, as well as the reasonable amount of use for the specific property. Failure to meet any of the requirements of the plan could result in a penalty.

If the drought eases enough to allow the DWP to revert to Phase 1 restrictions, the penalties would no longer apply.

A $40,000 penalty would mean that a customer had committed continuous violations over at least 18 months amid the most severe drought conditions — a highly unlikely scenario, Adams said.

The proposed amendments to the conservation plan must be approved by various governing bodies and might not go into effect before May 1, Adams said. The first fines would not appear until the middle of the summer, he added. All the money generated by the fines would go back into DWP’s conservation programs.

Dozens of water suppliers have built penalties or surcharges into their rates. But Matthew Buffleben, an official with the State Water Resources Control Board’s enforcement office, said Tuesday that he had not heard of any agency administering a flat fine for profligate use, as DWP is proposing.

Buffleben said his office has been asking water districts to reach out to their heaviest users and provide audits, but DWP’s plan “has taken it a step beyond that.”

Building financial penalties into DWP’s rate structure might have been more effective at slicing water usage, said Mark Gold, associate vice chancellor for environment and sustainability at UCLA. But California law makes it difficult for a utility to legally justify rates that increase as usage rises.

Former DWP Commissioner Jonathan Parfrey said the changes would send a message about equity.

“I think this is important so that the public realizes that the sacrifices they’re making are being shared by everyone across all economic classes,” said Parfrey, now executive director of the nonprofit group Climate Resolve.

For more on the California drought and water, follow me on Twitter @ByMattStevens